As a first background example, every year a number of people die victim of snow avalanches. The probability of survival for a snow buried victim is tightly related to the time spent for finding him or her.
In the state of the art, there are essentially two devices used to locate victims of avalanches: the ARB (Avalanche Rescue Beacon) and the RECCO system.
An ARB (Avalanche Rescue Beacon) system, or ARVA (Appareil de Recherche de Victimes d'Avalanches) or DVA (Detecteur de Victimes d'Avalanche) consists in a radiofrequency transmitter-receiver using a radio-frequency wave at 457 kHz. In emitting mode, the person wearing the device can be located. The same device is used in the receptor mode to locate the snow buried victim by rescuers or any person participating in the search.
The RECCO™ system is based on harmonic radar and transmits at around 1.8 GHz. This system is divided in two parts. The rescue teams are equipped with RECCO transmitters that emit a directional signal. The RECCO reflector worn by the potential victims reflects the signal and returns it to the receiver/transmitter.
Both ARVA and RECCO systems emit a signal and the localization is achieved, based on the power signal. Each device requires a specific training and learning of search techniques (dichotomy or triangulation methods). And more, they are technically limited in range and accuracy, so they require time and a large rescue team for finding the victim.
Another system is also known under the name SICRA (SICRA: a GNSS cooperative system for avalanche rescue, IEEE 2012), a GNSS cooperative system for avalanche rescue. This system integrates the GNSS navigation technologies, the cooperative networks and a control system for planning the actions of the rescue team. By acquiring the position of each element in the system, the system generates the relative distance in the snow between the buried victim and the rescuers and gives the direction that the rescuer has to follow for finding the victim. The system uses GPS positioning only which results in a reduced accuracy of the victim location. In addition, the system does not work in case of loss of the GPS signal for one reason or another.
Another system is based only on HSGPS (High Sensitivity Global Positioning System) (GPS tracking performance under avalanche deposited snow, 2006) receivers to locate avalanche victims at snow depths of two meters and beyond. This system tracks weaker GPS signals through avalanche snow. The GPS signal from the satellite to the receiver buried under the avalanche snow, may take a number of different paths depending on refraction and scattering when the signal encounters the snow. Thus, multipath reflections reduce the position accuracy and the precision of victim's localization, and so this system is still not adequate to quickly identify the position of the person completely trapped under snow avalanches.
Other examples of situations wherein the same difficulties to locate persons, animals or objects are: earthquakes, inundations, including tsunamis, boat accidents and losses of divers. Some of the same systems of the prior art may be used occasionally for trying to locate the victims, notably GNSS receivers. But they are still useful to a lesser extent, since these victims are seldom pre-equipped with a specific device. Also, in the water or under significant amount of displaced boulders, these techniques will seldom work.
Therefore, the systems and methods of the prior art have significant limitations in view of the problems which are encountered. There is thus a need for new techniques or methods to find a victim in a limited time with a better accuracy.
The present invention discloses a solution to overcome the previously cited drawbacks.